The broad, long-term objective of this research is to understand personal and environmental factors that influence interpersonal behavior by studying dyadic processes. Interpersonal phenomena occur between people in "interpersonal fields" instead of within people as is often assumed in individual differences research designs. The stability of an interpersonal field can be inferred from the predictability of transitions from antecedent to consequent communications with a dyad. Stable interpersonal field can be inferred from the predictability of transitions from antecedent to consequent communications with a dyad. Stable interpersonal fields are desirable because they are theoretically associated with consistent behavioral patterns, reduced anxiety, increased relatedness, and more enduring relationships. Interpersonal fields in sport coaching dyads provide an important context for this research. Coaching behaviors have been associated with mental health (e.g., self-esteem, fear of failure), physical activity has known self- esteem enhancing, anxiolytic, and anti-depressant effects, and coaches' interpersonal behaviors have been shown to perpetuate or reduce participation in physical activity. To study interpersonal fields, the Structural Analysis of Social Behavior, an interpersonal circumplex model that captures a broad spectrum of interpersonal behavior, will be used to code behavioral exchanges in coaching dyads during lessons, Several predictive principles associated with the SASB have been adapted to describe the full-range of possible transitions between antecedent and consequent communications according to their stability. Influences on the stability of dyadic interpersonal transitions, defined according to the SASB predictive principles, have not been investigated although previous research and preliminary data suggest that neuroticism, openness to experience, attachment style, and wishes to be self-loving may moderate the stability of these transitions. Establishing the influence of individual differences and individual difference similarities between members of a dyad on the stability of interpersonal transitions within that dyad will enhance understanding of factors that regulate interpersonal fields. This knowledge also will inform scientific and clinical efforts to promote optimal mental health and functioning.